A power supply apparatus, an electronic load device (active dummy load) and the like include a number of electric components. Some of such electric components generate a large amount of heat when supplied with current thereto. Hereinafter, such components are referred to as heat-generating components. It is desirable for heat-generating components to be cooled. An example of useable cooling techniques is a forced air cooling method. An example of power supply apparatuses employing a forced air cooling technique is disclosed in JP 2003-244958 A. The power supply apparatus disclosed in JP 2003-244958 A includes a rectangular-parallelepiped-shaped heat sink having two side surfaces to which first and second plate-shaped chassis are attached. Each of the chassis has a window therein. A semiconductor module, which is a heat-generating component, is mounted on the heat sink in such a manner as to protrude through each of the windows in the first and second chassis. On the surface of each of the first and second chassis opposite to the surface contacting the heat sink, a printed circuit board is disposed with a spacing disposed from the heat sink. The semiconductor modules are electrically connected to the printed circuit boards by means of connection terminals of the respective semiconductor modules. The heat sink, the first and second chassis, and the printed circuit boards form a block. The block has its lateral side covered by a case, and its front and rear sides are covered by front and rear panels, respectively. A fan, which feeds air, is mounted on the block on the rear panel side thereof. The first and second chassis on the opposite sides of the heat sink form, therebetween, a path for air cooling the semiconductor modules. The connection terminals on the semiconductor modules are located between the first chassis and the associated printed circuit board and between the second chassis and the associated printed circuit board, respectively, and are exposed to external air sucked in by the fan.
The connection terminals of the semiconductor modules of this power supply apparatus are adversely affected by undesirable components, if any, in external air sucked into the interior of the power supply apparatus, and, therefore, insulation of the semiconductor modules would be degraded. To prevent it, the semiconductor modules are so disposed that the insulation distance can be larger. However, when such power supply apparatus is used in electroplating, it will be in an environment in which a mist of liquid generated from a plating bath tank is flowing, and, therefore, even with a large insulation distance held, air containing the plating liquid mist should contact the connection terminals of the semiconductor modules, whereby the insulation is degraded. this could lead to failure of the modules. When the power supply apparatus is used in welding, it will be placed in an environment where electrically conductive dust and particles, such as iron particles, are floating. Such conductive particles would be sucked into the interior of the power supply apparatus, accumulate over the connection terminals of the semiconductor modules, and cause current leakage, which could lead to failure of the semiconductor modules.
An object of the present invention is to provide a cooling structure for a heat-generating component to prevent the heat-generating component from being broken down even when it is used in an environment tending to cause failure of such component.